PROJECT SUMMARY/ABSTRACT Pulsatile tinnitus (PT) is the perception of rhythmic sound without an external source. It is a debilitating symptom experienced by more than 5 million Americans. PT has very high rates of comorbid debilitating psychiatric illness that can typically be mitigated by treating the underlying cause of PT. Unfortunately, not all causes of PT are treatable and in many cases the current treatment methods may be more hazardous to patients' health than the underlying disease. The etiology of pulsatile tinnitus is known to be related to blood flow, however, to date, the specific features of hemodynamics that result in symptoms has not been established. This project plans to expand on new insights into features of the velocity field in the venous sinuses that our team has obtained using advanced MR velocity measurement method that indicate a link between patterns of blood flow and symptom presentation. These results indicate a consistent finding in patients with PT, namely regions of pronounced vorticity. In individuals with normal caliber vessels the vortex manifests in cases when the jugular bulb is high relative to the sigmoid sinus insertion. In individuals with irregular venous caliber, such as diverticulums and stenoses, regions of vortex swirling in and adjacent to these irregularities are noted. In this project we will conduct a systematic study that will first develop improved MR methods for measuring the velocity field. These will be based on validation in carefully characterized flow models. Undersampling methods (with advanced reconstruction) that substantially reduce acquisition time will be implemented. The most favorable methods will then be used to image flow patterns in two classes of subjects: Normals and those with PT who have regular caliber vessels across the spectrum of geometric variability in the venous sinuses; and patients who have irregular flow lumens (diverticulums and/or stenoses.) We believe that successful conduct of this study will set the stage for a more comprehensive investigation of PT that would include the use of Computational Fluid Dynamics to interrogate features that cannot be easily manipulated in vivo, and that can be used to simulate the sound generation associated with hemodynamic features. We also consider that there would be a role for inclusion of the measurement of turbulent kinetic energy (under investigation in our laboratory) in this condition. We believe that this project will provide a basis for providing new insights into the physiology underlying sound generation from the venous sinuses. This information will provide guidance to interventionalists who wish to develop novel and safer treatment methods, including design of new devices, to treat adverse conditions in the cerebral vascular structures near the hearing apparatus thought to be the underlying cause of PT.